RU2510931C2 - Display device - Google Patents

Abstract

FIELD: physics, optics.

SUBSTANCE: invention relates to a display device equipped with an optical sensor in a pixel region. Display device has optical sensor having a highly sensitive photosensitive element. The photosensitive element is provided with a diode (D1), reset signal wiring (RST) that supplies a reset signal, readout signal wiring (RWS) that supplies a readout signal, a storage node whose potential (V_INT) changes in accordance with the amount of light received by the diode (D1) in the period from when the reset signal is supplied until when the readout signal is supplied, an amplification element (C1) that amplifies the potential (V_INT) in accordance with the readout signal, and a sensor switching element (M2) for reading out the potential amplified in the output wiring. The potential of the screening film (LS), provided on the back surface of the diode, is fixed equal to a constant potential (V_LS) which satisfies the following relationship: V_LS≥V_RST.H.

EFFECT: high sensitivity and high signal-to-noise ratio in a photosensor.

17 cl, 63 dwg

Description

2420-184876EN / 085

FIELD OF THE INVENTION

The present invention relates to a display device equipped with an optical sensor having a photosensitive element, for example, a photodiode or a phototransistor, and, in particular, relates to a display device equipped with an optical sensor in the pixel region.

BACKGROUND

Traditionally, a display device equipped with an optical sensor has been proposed, which is equipped with photodetector elements, such as, for example, photodiodes in its pixels, and which is therefore able to detect the brightness of external illumination and register an image of an object approaching its display panel.

Such a display device equipped with an optical sensor is intended to be used as a display device for two-way communication or as a display device with a touch panel function. In the case of a conventional display device equipped with an optical sensor, when known components, such as signal lines and scan lines, TFT (thin film transistors) and pixel electrodes are formed on the active matrix substrate using semiconductor material processing technology, then photodiodes, etc. P. formed on the active matrix substrate using the same technology (see JP 2006-3857A).

Since a conventional optical sensor is formed on the active matrix substrate, the exemplary configuration disclosed in W0 2007/145346 and W0007 / 145347 is shown in FIG. 62. The conventional optical sensor shown in FIG. 62, consists of the following main components: photodiode D1, capacitor C2, and transistor M2. An RST line is connected to the anode D1 of the photodiode to provide a reset signal. One of the electrodes of the capacitor C2 and the gate of the transistor M2 are connected to the cathode of the photodiode D1. The drain of the transistor M2 is connected to the VDD line, and its source is connected to the OUT line (output). The other electrode of the capacitor C2 is connected to the RWS line for supplying a read signal.

In this configuration, the sensor output signal V _PIX corresponding to the amount of light received by the photodiode D1 can be obtained by supplying a reset signal and a read signal to the RST line and the RWS line, respectively, at respective predetermined times. Here, the operation of the conventional optical sensor shown in FIG. 62 is explained with reference to FIG. 63. It should be noted that in FIG. 63 a low level (equal to, for example, -7 V) of the reset signal is indicated as "V _RST.L ", a high level (equal to, for example, 0 V) of the reset signal is indicated as "V _RST.H ", a low level (equal to, for example , 0 V) of the read signal is indicated as "V _RWS.L ", and a high level (equal to, for example, 15 V) of the read signal is indicated as "V _RWS.H ".

First, when line RST is supplied V _RST.H reset signal with a high level, photodiode D1 has a forward bias, and therefore, the potential V _INT M2 gate transistor is expressed by the following formula (1):

V _INT = V _RST.H -V _F , (1)

where V _F is the forward voltage of the photodiode D1. Since V _INT here is lower than the threshold voltage of the transistor M2, the transistor M2 is non-conductive during the reset period.

Then, the reset signal becomes again having a low-level potential V _RST.L (at time t _RST, shown in FIG. 63), and therefore starts the photocurrent integration period (registration period which is a period designated T _INT, which is shown in Fig. 63). During the integration period, a photocurrent proportional to the amount of light incident on the photodiode D1 flows from the capacitor C2, as a result of which the capacitor C2 is discharged. Accordingly, the gate potential V _{INT of the} transistor M2 at the end of the integration period is expressed by the following formula (2):

V _INT = V _RST.H -V _F -ΔV _RST · C _PD / C _TOTAL -I _PHOTO · T _INT / C _TOTAL , (2)

where ΔV _RST is the height of the reset signal pulse (V _RST.H -V _RST.L ), I _PHOTO is the photocurrent of photodiode D1, and T _INT is the duration of the integration period. C _PD is the capacitance of the photodiode D1. C _TOTAL - the sum of the capacitance of the capacitor C2, the capacitance C _{PD of the} photodiode D1 and the capacitance C _{TFT of the} transistor M2. Moreover, during the integration period, since V _INT is lower than the threshold voltage of the transistor M2, the transistor M2 is non-conductive.

After the integration period at time t _RWS shown in FIG. 63, the read signal level RWS rises, and therefore, the read period begins. It should be noted that the read period continues until the read signal level RWS remains high. In this case, charges are injected into the capacitor C2. As a result, the gate potential V _{INT of the} transistor M2 is expressed by the following formula (3):

V _INT = V _RST.H -V _F -ΔV _RST · C _PD / C _TOTAL -I _PHOTO · T _INT / C _TOTAL + ΔV _RWS · C _INT / C _TOTAL , (3)

where ΔV _RWS is the height of the read signal pulse (V _RST.H -V _RWS.L ). In this case, the gate potential V _{INT of the} transistor M2 becomes higher than its threshold voltage, and this causes the transistor M2 to become conductive. Thus, the transistor M2, together with the bias transistor M3 provided at the end of the OUT line in each column, function as a source follower amplifier. In other words, the output voltage V _{PIX of the} sensor from the transistor M2 is proportional to the integral of the photocurrent of the photodiode D1 during the integration period.

It should be noted that in FIG. 63, the waveform indicated by the solid line represents the change in potential V _INT when the amount of light incident on the photodiode D1 is small. The waveform indicated by the dashed line represents the change in potential V _INT when the amount of light incident on the photodiode D1 is at a saturation level. The ΔV _SIG value shown in FIG. 63 is a potential difference proportional to the amount of light incident on the photodiode D1. The value ΔV _INT shown in FIG. 63 is the amount by which the potential V _INT rises when a read signal from the RWS line is supplied to the optical sensor during the read period.

SUMMARY OF THE INVENTION

In the above-described display device having an optical sensor in a pixel, the difference between the respective potentials of the storage node in cases with different illumination values (for example, in the case of a dark state and in the case when light falls at the saturation level) at the end of the accumulation period is equal to the difference between the corresponding potentials of the accumulation node in the above relevant cases after their amplification during the reading period. In other words, the difference between the potential (indicated here as "V _INT1 ") of the storage node at the end of the accumulation period in the case of a dark state and the potential (indicated here as "V _INT1 ") of the storage node at the end of the accumulation period when light falls on the saturation level is equal to the difference between the potential (indicated here as "V _INT3 ") of the storage node after its amplification during the reading period in the case of a dark state and the potential (indicated here as "V _INT3 ") of the storage node after its amplification during a different reading period when light is incident at the saturation level.

However, since the difference described above between V _INT3 and V _INT4 is larger, an optical sensor can be obtained having excellent characteristics, for example, higher sensitivity and a higher signal to noise ratio. Therefore, it is an object of the present invention to provide a display device having a highly sensitive optical sensor by establishing a greater difference between the potentials (V _INT3 -V _INT4 ) of the storage unit after amplification due to the difference in illumination on the light receiving surface than the difference between its potentials (V _INT1 -V _INT2 ) at the end of the integration period.

In order to achieve the above-described object, the display device disclosed herein is a display device that includes an optical sensor in a pixel region on an active matrix substrate, this optical sensor including: a photodetector for receiving incident light; a reset signal line for supplying a reset signal to the optical sensor; a read signal line for supplying a read signal to the optical sensor; a storage unit having a potential that varies depending on the amount of light received by the photodetector during the recording period, the recording period being the period from the moment the reset signal is supplied until the read signal is supplied; an amplifier element for enhancing the potential of the storage node in accordance with the read signal; and a sensor switching element for sensing a potential amplified by the amplifying element, and outputting this potential as an output signal from the sensor circuit to an output line in which a light shielding film is provided on a side opposite to the light receiving surface relative to the photodetector, this light shielding film connected to a power source for supplying voltage to fix the potential of the light shielding film equal to a constant potential, and the following is satisfied Single formula:

V _LS ≥V _RST.H ,

where V _LS is the constant potential and V _RST.H is the high-level potential of the reset signal.

In the configuration described above, in which an amplifier element is provided for amplifying the potential of the storage unit in accordance with the read signal, the difference between the potentials of the storage unit due to the difference between the illumination values on the light-receiving surface after amplification is larger than the difference between its potentials at the end of the integration period. For example, the difference between the potential of the storage node after its amplification during the reading period in the case of a dark state and the potential of the storage node after its amplification during the reading period when light falls at the saturation level is greater than the difference between the potential of the storage node in the end of the accumulation period in the case of a dark state and the potential of the storage node at the end of the accumulation period in the case when light falls at the saturation level. Therefore, a display device including an optical sensor with high sensitivity can be implemented. Further, by establishing the potential of the light shielding film as a constant potential equal to or greater than the high level potential of the _reset signal V _RST.H , a sensor output signal having excellent linearity with respect to the amount of incident light can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

In FIG. 1 is a block diagram schematically showing a configuration of a display device according to one embodiment of the present invention.

In FIG. 2 is an equivalent circuit diagram showing a configuration of one pixel in a display device according to a first embodiment of the present invention.

In FIG. 3 shows the capacitance-voltage (CV) characteristics of a capacitor equipped with an optical sensor according to a first embodiment of the invention.

In FIG. 4 is a timing chart showing a waveform of a control signal and a change in potential of a storage unit in an optical sensor according to a first embodiment of the invention.

In FIG. 5 is an equivalent circuit diagram of an optical sensor according to this embodiment of the invention.

In FIG. 6 is a plan view showing an exemplary planar structure of an optical sensor according to this embodiment of the invention.

In FIG. 7 is an enlarged view of the region where the capacitor C1 is formed.

In FIG. 8 is a schematic cross-sectional view showing a connection diagram of respective regions in an optical sensor according to this embodiment of the invention.

In FIG. 9 is a signal timing chart showing a change in potential V _{INT of the} storage node from the end of the integration period to the reading period.

In FIG. 10A is a schematic cross-sectional view showing charge transfer in capacitor C1 when the potential of the gate electrode is lower than the threshold voltage.

In FIG. 10B is a schematic cross-sectional view showing charge transfer in capacitor C1 when the potential of the gate electrode is higher than the threshold voltage.

In FIG. 11 is a schematic cross-sectional view showing a pin diode having a lateral structure.

In FIG. 12A is a graph of the characteristic “I _d versus V _LS ”, showing the differences between the three modes of operation of the pin diode.

In FIG. 12B is a graph of the characteristic “I _d versus V _LS ”, showing the differences between the three modes of operation of the pin diode.

In FIG. 13 is a graph showing the relationship between the potential V _{A of the} anode and the potential V _{LS of the} light shielding film LS.

In FIG. 14 is a timing chart showing a reading moment in a display device according to a first embodiment of the invention.

In FIG. 15 is a circuit diagram showing an internal configuration of a pixel reading circuit equipped with a sensor.

In FIG. 16 is a signal timing chart showing a relationship between a read signal, a sensor output signal and an output signal from a pixel reading circuit equipped with a sensor.

In FIG. 17 is an equivalent circuit diagram schematically showing a configuration of a sensor column amplifier.

In FIG. 18 is an equivalent circuit diagram of an optical sensor according to a second embodiment of the invention.

In FIG. 19 is a signal timing chart showing a reset signal and a read signal supplied to an optical sensor according to a second embodiment of the invention.

In FIG. 20 is a plan view illustrating an exemplary planar structure of an optical sensor according to a second embodiment of the invention.

In FIG. 21 is an enlarged view of the region shown in FIG. 20, where the capacitor C1 is formed.

In FIG. 22 is a schematic cross-sectional view showing a connection diagram of corresponding regions in an optical sensor according to a second embodiment of the invention.

In FIG. 23 is an equivalent circuit diagram of an optical sensor according to a third embodiment of the invention.

In FIG. 24 is a plan view showing an exemplary planar structure of an optical sensor according to a third embodiment of the invention.

In FIG. 25 is an enlarged view of the region shown in FIG. 24, in which a capacitor C1 is formed.

In FIG. 26 is a schematic cross-sectional view showing a connection diagram of respective regions in an optical sensor according to a third embodiment of the invention.

In FIG. 27 is an equivalent circuit diagram of an optical sensor according to a fourth embodiment of the invention.

In FIG. 28 is a plan view showing an exemplary planar structure of an optical sensor according to a fourth embodiment of the invention.

In FIG. 29 is an enlarged view of the region shown in FIG. 28, where a p-channel TFT is formed.

In FIG. 30 is a schematic cross-sectional view showing a connection diagram of respective regions in an optical sensor according to a fourth embodiment of the invention.

In FIG. 31 is an equivalent circuit diagram of a p-channel TFT optical sensor according to a fourth embodiment of the invention.

In FIG. 32 is a timing diagram of the signals showing the effects that stray capacitance and leakage current exert on the potential of the storage unit.

In FIG. 33 is a plan view showing an exemplary planar structure of an exemplary modified embodiment of an optical sensor according to a fourth embodiment of the invention.

In FIG. 34 is an enlarged view of the region shown in FIG. 33, where a p-channel TFT is formed.

In FIG. 35 is an equivalent circuit diagram of the p-channel TFT shown in FIG. 33.

In FIG. 36 is an equivalent circuit diagram of an optical sensor according to a fifth embodiment of the invention.

In FIG. 37 is a plan view showing an exemplary planar structure of an optical sensor according to a fifth embodiment of the invention.

In FIG. 38 is an enlarged view of the region where an amplification element (n-channel TFT) is formed in the fifth embodiment.

In FIG. 39 is a schematic cross-sectional view showing a connection diagram of corresponding regions in an optical sensor according to a fifth embodiment of the invention.

In FIG. 40 is an equivalent circuit diagram of an n-channel TFT serving as an amplifier element in a fifth embodiment of the invention.

In FIG. 41 is a plan view showing an exemplary planar structure of an exemplary modified embodiment of an optical sensor according to a fifth embodiment of the invention.

In FIG. 42 is a schematic cross-sectional view illustrating a connection diagram of respective regions in the reinforcing element in the exemplary modified embodiment shown in FIG. 41.

In FIG. 43 is an equivalent circuit diagram of the n-channel TFT shown in FIG. 42.

In FIG. 44 is an equivalent circuit diagram of an optical sensor according to a sixth embodiment of the invention.

In FIG. 45 is a plan view illustrating an example planar structure of an optical sensor according to a sixth embodiment of the invention.

In FIG. 46 is an enlarged view of the region where an amplifier element (diode D2) is formed in a sixth embodiment of the invention.

In FIG. 47 is a schematic cross-sectional view showing a connection diagram of respective regions in an optical sensor according to a sixth embodiment of the invention.

In FIG. 48 is an equivalent circuit diagram of a diode serving as an amplifier element according to a sixth embodiment of the invention.

In FIG. 49 is an equivalent circuit diagram of an optical sensor according to a first modified embodiment of a sixth embodiment of the invention, which is given as an example.

In FIG. 50 is a plan view showing an exemplary planar structure of an optical sensor according to a first modified embodiment of a sixth embodiment of the invention, which is given as an example.

In FIG. 51 is an equivalent circuit diagram of an optical sensor according to a second modified embodiment of a sixth embodiment of the invention, which is given as an example.

In FIG. 52 is a plan view showing an exemplary planar structure of an optical sensor according to a second modified embodiment of a sixth embodiment of the invention, which is given as an example.

In FIG. 53 is an equivalent circuit diagram of an optical sensor according to a seventh embodiment of the invention.

In FIG. 54 is a plan view showing an exemplary planar structure of an optical sensor according to this embodiment of the invention.

In FIG. 55A is a circuit diagram illustrating a state of charge injection in the case where a series-connected capacitor C _{SER is} combined with a configuration in which a variable capacitor is an amplifying element.

In FIG. 55B is a circuit diagram showing a state of charge injection in the case where a series-connected capacitor C _{SER is} combined with a configuration in which the p-channel TFT is an amplifier element.

In FIG. 56 is an equivalent circuit diagram of an optical sensor according to an eighth embodiment of the invention.

In FIG. 57 is a plan view showing an exemplary planar structure of an optical sensor according to an eighth embodiment of the invention.

In FIG. 58 is an equivalent circuit diagram of an optical sensor according to a ninth embodiment of the invention.

In FIG. 59 is a plan view illustrating an example planar structure of an optical sensor according to a ninth embodiment of the invention.

In FIG. 60 is an equivalent circuit diagram of an optical sensor according to this embodiment of the invention.

In FIG. 61 is a plan view illustrating an example planar structure of an optical sensor according to this embodiment of the invention.

In FIG. 62 is an equivalent circuit diagram showing an example of a conventional optical sensor formed on an active matrix substrate.

In FIG. 63 is a timing chart showing the shape of the control signal and the potential change of the storage node in a conventional optical sensor.

DETAILED DESCRIPTION OF THE INVENTION

A display device according to one embodiment of the present invention is a display device including an optical sensor in a pixel region on an active matrix substrate, in which the optical sensor includes: a photodetector for receiving incident light; a reset signal line for supplying a reset signal to the optical sensor; a read signal line for supplying a read signal to the optical sensor; a storage unit having a potential that varies depending on the amount of light received by the photodetector during the recording period, the recording period being the period from the moment the reset signal is supplied until the read signal is supplied; an amplifier element for enhancing the potential of the storage node in accordance with the read signal; and a sensor switching element for sensing a potential amplified by the amplifying element and outputting this potential as an output signal from the sensor circuit to the output line.

In this configuration, in which an amplifier element is provided for amplifying the potential of the storage unit in accordance with the read signal, the difference between the potentials of the storage unit is due to the difference in illumination values on the light receiving surface after the gain is greater than the difference between its potentials at the end of the integration period. For example, the difference between the potential of the storage unit after amplification during the reading period in the case of a dark state and the potential of the storage unit after amplification during the reading period when light falls at the saturation level is greater than the difference between the potential of the storage unit at the end of the period accumulation in the case of a dark state and the potential of the storage node at the end of the accumulation period in the case when light is incident at the saturation level. It should be noted that this function of amplifying the potential difference is established between any illumination values, and not exclusively for the case of a dark state and for the case when light falls at the saturation level. In this manner, a display device including an optical sensor with high sensitivity can be created.

In addition, the configuration described above is preferably modified so that a light shielding film is provided on a side opposite the side of the light receiving surface with respect to the photodetector element, this light shielding film being connected to a power supply for supplying voltage to fix the potential of the light shielding film to a constant potential, and the following formula is satisfied :

V _LS ≥V _RST.H ,

where V _LS is the constant potential and V _RST.H is the high-level potential of the reset signal. In this preferred configuration, fluctuations in the potential of the light shielding film can be eliminated, whereby the degradation of the characteristics of the diode D1 can be mitigated.

In the case where a pin diode is used as the photodetector, it is even more preferable that the following formula is satisfied:

V _LS ≥V _RST.H + V _{th_p} ,

where V _{th_p} is the threshold voltage of the p-channel pin diode. This preferred configuration may cause the pin diode to operate in a state in which free electrons and positive holes tend to migrate in the diode at both boundaries of the intrinsic semiconductor layer (i-layer) from the p-layer and from the n-layer. Therefore, the photocurrent (photoelectric current) increases, and the linearity of the change in the photocurrent (photoelectric current) with changing illumination can be improved.

In the display device described above, for example, a variable capacitor can be used as an amplifying element. In this case, for example, a MOS capacitor (metal-oxide-semiconductor capacitor) can be used as a variable capacitor, which includes a read signal line, an insulating film, and a p-type semiconductor region formed in a silicon film. Alternatively, a MOS capacitor may be used as a variable capacitor, which includes a gate electrode of a sensor switching element, an insulating film, and an n-type semiconductor region formed in the silicon film. In the configuration described above, the read signal line can be used as a gate of a variable capacitor. Therefore, this configuration has the advantage of not having to provide a line and contacts for connecting the read signal line and the gate electrode.

Moreover, in the above-described display device, for example, a p-channel thin-film transistor can be used as an amplifying element. In this case, it is preferable that in the p-channel thin-film transistor, the channel region is formed in a wide area of the silicon film connecting the photodetector element and the storage unit to each other, and so that the gate electrode of the p-channel thin-film transistor is created so that it covers this wide area . In this configuration, the boundary length can be reduced, which prevents narrowing of the dynamic range due to stray capacitance or leakage current. Alternatively, an n-channel thin film transistor may be used as an amplifier element in the display device described above.

Alternatively, a diode having a gate electrode on a channel may be used as an amplifying element in the display device described above. In this configuration, the border length can be reduced.

In addition, as another preferred configuration, the display device described above may have a configuration in which an electrode opposite to the light shielding film is provided to form a capacitively connected capacitance relative to the stray capacitance between the light shielding film and the photodetector, and this electrode is electrically connected to the signal line reading out. This configuration has the effect of reducing the influence that the parasitic capacitance between the light-shielding film and the photodetector has on the potential change of the storage unit during the integration period.

In addition, in the above-described display device, it is preferable to provide a plurality of photodetector elements in the pixel region, moreover, the plurality of photodetector elements are connected in parallel and the amplifying element is connected to one of the photodetector elements located at the end of the photodetector elements. Due to the parallel connection of the plurality of photodetector elements in this way, the photoelectric current can be increased, whereby the sensitivity can be improved.

In the display device described above, the sensor switching element is preferably a switching element with three terminals, the gate electrode being one of the three terminals being connected to the storage unit, and one of the other two terminals of the three terminals being connected to the output line. In this configuration, a single sensor switching element is sufficient, and therefore, the configuration of the optical sensor circuit can be simplified. It should be noted that in the display device described above, a switching element can be additionally provided for resetting the sensor switching element.

In the display device described above, the amplifier element preferably has a threshold potential at which the state of the amplifier element switches between an “on” (“ON”) state and an “off” (OFF) state between the low level potential and the high level read signal potential.

The display device described above can be implemented as a liquid crystal display device, which further includes an opposite substrate, which is the opposite of the active matrix substrate; and liquid crystal located between the active matrix substrate and the opposite substrate.

The following is an explanation of more specific embodiments of the present invention with reference to the drawings. It should be noted that in the following embodiments, exemplary configurations are shown when the display device of the present invention is implemented as a liquid crystal display device, but the display device of the present invention is not limited to the liquid crystal display device, and the present invention is applicable to arbitrary a display device using an active matrix substrate. It should be noted that a display device according to the present invention having optical sensors is used as a display device equipped with a touch panel that detects an object approaching its screen and performs an input operation as a display device for two-way communication having a display function and image capture function, etc.

In addition, for the convenience of explanation in the drawings, the references to which are given below, of the constituent elements included in an embodiment of the present invention, only those basic elements are simplified, the illustrations of which are necessary to explain the present invention. Therefore, the display device according to this embodiment of the invention may include arbitrary elements not shown in the drawings, referred to in the description of the present invention. In addition, the dimensions of the elements shown in the drawings do not accurately reflect the actual dimensions of the constituent elements, aspect ratios of the constituent elements, etc.

[First embodiment of the invention]

First, an explanation is given of the configuration of the active matrix substrate that is provided in the liquid crystal display device according to the first embodiment of the present invention, with reference to FIG. 1 and FIG. 2.

In FIG. 1 is a block diagram schematically illustrating a configuration of an active matrix substrate 100 that is equipped with a liquid crystal display device according to one embodiment of the present invention. As shown in FIG. 1, the active matrix substrate 100 includes, on its glass substrate, at least a region of 1 pixels, a driver 2 of the gate of the display device, a driver 3 of the source of the display device, a driver of 4 sensor columns, a driver of 5 sensor columns, a buffer amplifier 6, and a connector 7 for flexible printed circuit boards (FPC connector). In addition, a signal processing circuit 8 is connected to the active matrix substrate 100 through an FPC connector 7 and a flexible printed circuit board (FPC) 9 for processing an image signal recorded by a photodetector (described below) in the pixel region 1.

It should be noted that the constituent elements described above on the active matrix substrate 100 can be formed integrally on a glass substrate by using semiconductor material processing technology. In an alternative embodiment, the configuration may be as follows: amplifiers and drivers from the elements described above are mounted on a glass substrate, for example, by COG methods (mounting a chip on glass). In addition, in an alternative embodiment, at least a portion of the above elements shown on the active matrix substrate 100 in FIG. 1 can be mounted on a flexible printed circuit board (FPC) 9. The active matrix substrate 100 is coated with an opposite substrate (not shown) having a counter electrode formed on its entire surface to form a multilayer structure. The liquid crystal material is sealed in the space between the active matrix substrate 100 and the opposite substrate.

The pixel region 1 is an area where a plurality of pixels are formed for displaying images. In this embodiment, an optical sensor for recording images is provided in each pixel in the region of 1 pixels. In FIG. 2 is an equivalent circuit diagram showing the arrangement of pixels and optical sensors in the 1 pixel region on the active matrix substrate 100. In the example shown in FIG. 2, one pixel is formed of three sub-pixels R (red), G (green) and B (blue). In one pixel made up of these three subpixels, one optical sensor is provided. The pixel region 1 includes pixels arranged in a matrix of M rows × N columns and optical sensors arranged in a similar manner in a matrix of M rows × N columns. It should be noted that the number of subpixels is M × 3N, as described above.

Therefore, as shown in FIG. 2, the pixel regions 1 have gate lines GL and source lines COL arranged orderly in a matrix as pixel lines. The shutter lines GL are connected to the driver 2 of the shutters of the display device. The source COL lines are connected to the driver 3 of the source of the display device. It should be noted that in the area of 1 pixel provided M lines of lines of GL shutters. Below, when it is necessary to describe a specific individual line of gates of gates, it is denoted as GLi (i = 1 to M). On the other hand, three source COL lines per pixel are provided for supplying image data to three sub-pixels in a pixel, as described above. When it is necessary to describe a specific individual line of COL sources, it is designated as COLrj, COLgj or COLbj (j = 1 to N).

At each of the intersection points of the gate lines GL and the source COL lines, a thin film transistor (TFT) M1 is provided as a switching element for the pixel. It should be noted that in FIG. The 2 thin-film transistors M1 provided for the red, green, and blue sub-pixels are designated respectively as M1r, M1g, and M1b. The gate electrode of the thin film transistor M1 is connected to the gate line GL, its source electrode is connected to the source line COL, and its drain electrode is connected to a pixel electrode, which is not shown. Thus, as shown in FIG. 2, a liquid crystal capacitor C _{LC is} formed between the drain electrode of the thin film transistor M1 and the counter electrode (VCOM). In addition, an auxiliary capacitor C _{LS is} formed between the drain electrode and the TFT COM.

In FIG. 2, a red color filter corresponding to this subpixel is provided for a subpixel driven by a thin film transistor M1r that is connected to an intersection point of one gate line GLi and one source line COLrj. This subpixel is supplied with red image data from the driver 3 of the source of the display device through the source COLrj, whereby it functions as a red subpixel. In addition, for the subpixel driven by the thin film transistor M1g, which is connected to the intersection of the gate line GLi and the source line COLgj, a green color filter corresponding to this subpixel is provided. This subpixel is supplied with green image data from the driver 3 of the source of the display device through the line COLgj of sources, whereby it functions as a green subpixel. In addition, for the subpixel driven by the thin film transistor M1b, which is connected to the intersection of the gate line GLi and the source line COLbj, a blue color filter corresponding to this subpixel is provided. This subpixel is supplied with blue image data from the driver 3 of the source of the display device through the line COLbj of sources, whereby it functions as a blue subpixel.

It should be noted that in the example shown in FIG. 2, optical sensors are provided such that one optical sensor corresponds to one pixel (three sub-pixels) in the region of 1 pixels. However, the ratio between the pixels and the provided optical sensors is not limited to this example, but is arbitrary. For example, one optical sensor per each subpixel can be provided, or one optical sensor per multiple pixels can be provided.

As shown in FIG. 2, the optical sensor includes a photodiode D1 as a photodetector element, a capacitor C1 (an amplifying element), and a transistor M2. The capacitor C1, which in this embodiment functions as an amplifying element, is a variable capacitor.

In the example shown in FIG. 2, the source line COLr also functions as a VDD line for supplying a constant voltage VDD to the optical sensor from the driver 4 sensor columns. In addition, the source line COLg also functions as an OUT line for outputting the sensor output.

An RST line is connected to the anode of photodiode D1 to provide a reset signal. One of the electrodes of the capacitor C1 and the gate of the transistor M2 are connected to the cathode of the photodiode D1. The drain of the transistor M2 is connected to the VDD line, and its source is connected to the OUT line. In FIG. 2, a connection point (storage node) at which (in which) the cathode of the photodiode D1, one of the electrodes of the capacitor C1 and the gate of the transistor M2 are connected, is indicated as "INT". The other electrode of capacitor C1 is connected to the RWS line to provide a read signal. RST lines and RWS lines are connected to a 5-line sensor driver. The availability of these RST and RWS lines is provided for each row. Therefore, below, when you need to distinguish between these lines, they are denoted as RSTi and RWSi (i = 1 to M).

The sensor line driver 5 selects the RSTi and RWSi lines in the combination shown in FIG. 2, sequentially at given intervals t _{row of} time. Thus, the rows of optical sensors from which it is necessary to read information charges are selected sequentially in the region of 1 pixels.

It should be noted that, as shown in FIG. 2, the drain of the insulated gate field effect transistor M3 is connected to the end of the line OUT. An output line SOUT is connected to the drain of transistor M3. Therefore, the potential V _{SOUT of the} drain of the transistor M3 is output as an output signal from the optical sensor to the driver 4 columns of sensors. The source of the transistor M3 is connected to the VSS line. The gate of the transistor M3 is connected to a voltage reference source (not shown) through the voltage reference line VB.

In FIG. 3 shows a capacitance-voltage (CV) diagram of capacitor C1. In FIG. 3, the horizontal axis shows the voltage V _CAP between the electrodes of capacitor C1, and the vertical axis shows the electrostatic capacitance. As shown in FIG. 3, the capacitor C1 is characterized in that it has an electrostatic capacitance which is constant when the voltage V _CAP between the electrodes is small, but changes abruptly immediately before and after the voltage V _CAP between the electrodes reaches a threshold value. Therefore, the characteristics of the capacitor C1 can dynamically change when the potential of the read signal supplied from the RWS line changes. Using a capacitor C1 having such characteristics allows the optical sensor according to this embodiment to read the amplified value of the potential change of the storage node of the integration period T _INT , as shown in FIG. 4. The example shown in FIG. 4 is just one embodiment of the invention in which the low level V _{RST.L of} the reset signal is -1.4 V and the high level V _{RST.H of} the reset signal is 0 V. The low level V _{RWS.L of} the read signal is -3 V, and the high level V _{RWS.H of} the read signal is 12 V. Moreover, in FIG. 4, the waveform indicated by the solid line represents the change in potential V _INT in the case when the amount of light incident on the photodiode D1 is small, and the waveform indicated by the dashed line represents the change in potential V _INT in the case when the photodiode D1 light falls at saturation level. ΔV _SIG is the potential difference proportional to the amount of light incident on the photodiode D1. From a comparison between the conventional example shown in FIG. 63, and the configuration shown in FIG. 4, it is clear that in the optical sensor according to this embodiment, the change in the potential of the storage unit during the integration period T _INT in the case where light is incident at the saturation level is smaller than in a conventional optical sensor. However, the optical sensor according to this embodiment of the invention amplifies the potential of the storage node and reads it during the reading period (the period when the potential of the reading signal has a high level V _RWS.H ).

Here, the reading of the sensor output from the pixel region 1 is explained with reference to FIG. 4. First, when the level of the reset signal supplied from the driver of 5 lines of sensors to the RST line rises from a low level (V _RST.L ) to a high level (V _RST.H ), the photodiode D1 has a forward bias. As a result, the potential V _{INT of} the connection point INT has a value that is expressed by the following formula (4):

V _INT = V _RST.H -V _F , (4)

where V _F is the forward voltage of the photodiode D1. Since here, V _INT is lower than the threshold voltage of the transistor M2, the transistor M2 is non-conductive during the reset period.

Then, when the level of the reset signal returns to a low level V _RST.L , the integration period of the photoelectric current (T _INT ) begins. During the integration period T _INT , a photoelectric current proportional to the amount of light incident on the photodiode D1 flows into the capacitor C1, whereby the capacitor C1 is discharged. This leads to the fact that the potential V _{INT of} the connection point INT at the end of the integration period T _INT has a value that is expressed by the following formula (5):

V _INT = V _RST.H -V _F -∆V _RST · C _PD / C _TOTAL -I _PHOTO · t _INT / C _TOTAL (5)

where ΔV _RST is the pulse height of the reset signal (V _RST.H - V _RST.L ); I _PHOTO - photoelectric current of the photodiode D1; t _INT is the duration of the integration period; C _PD is the capacitance of the photodiode D1; and C _TOTAL is the capacitance of the entire optical circuit as a whole, that is, the total capacitance of the connection point INT equal to the sum of the capacitance C _{INT of the} capacitor C1, the capacitance C _{PD of the} photodiode D1 and the capacitance C _{TFT of the} transistor M2. Moreover, during the integration period also, since V _INT is lower than the threshold voltage of the transistor M2, the transistor M2 is non-conductive.

After the end of the integration period, the level of the read signal supplied to the RWS line rises, and the read period begins. In this case, electric charges are injected into capacitor C1. When the potential V _{INT of} the connection point INT becomes higher than the threshold voltage of the transistor M2, the transistor M2 becomes conductive. Therefore, the transistor M2 together with the bias transistor M3, which is provided at the end of the OUT line in each column, functions as an amplifier on the source follower. In the optical sensor according to this embodiment, the voltage of the output signal from the output line SOUT from the drain of the transistor M3 is equivalent to the value obtained by amplifying the photoelectric current integral of the photodiode D1 during the integration period. A description of the principles of this is given below.

As described above, in this embodiment, initialization by a reset pulse, integration of the photoelectric current during the integration period, and reading of the sensor output during the reading period, which are assumed to be one cycle, are performed cyclically.

The specific configuration of an optical sensor according to this embodiment of the invention is explained below with reference to the drawings. In FIG. 5 is an equivalent circuit diagram of an optical sensor according to a fifth embodiment of the invention. In FIG. 6 is a plan view showing an exemplary planar structure of an optical sensor according to this embodiment of the invention. In FIG. 7 is an enlarged view of the region where the capacitor C1 is formed. In FIG. 8 is a schematic cross-sectional view showing a connection diagram of respective regions in an optical sensor according to this embodiment of the invention.

As shown in FIG. 5, an optical sensor according to this embodiment of the invention includes a capacitor C1, which is a variable capacitor, as an amplifier element. In this embodiment, the capacitor C1 is a p-channel MOS capacitor. It should be noted that in FIG. 6, a transistor M2 is provided in the region between the source lines COLg and COLb, and two sets of capacitor C1 and diode D1 are provided, respectively, on both sides thereof. Alternatively, only one set of capacitor C1 and diode D1 can be provided. On the back side of the diode D1, a light-shielding film LS is provided to prevent light from falling from the backlight on the diode D1. The light-shielding film LS has a potential that is fixed to a constant potential V _LS , at least during operation of the optical sensor.

By fixing the potential of the light shielding film LS to the constant potential V _LS , the reliability of the photodiode can be improved. In the case where the potential of the light-shielding film LS is floating, deviations of the potential of the light-shielding film LS from the initial value are possible due to the transfer of charge carriers or injection, due to which a change and deterioration of the characteristics of diode D1 can occur. However, this problem can be solved by fixing the potential of the light-shielding film LS equal to the constant potential V _LS .

In addition, differences in characteristics between a plurality of D1 diodes can be reduced. This is because if the potential of the light-shielding film LS is floating, then the light-shielding film LS can have different floating potentials due to uneven charging of plasma ions, etc. in process of treatment. In contrast, this problem can be solved by fixing the potential of the light-shielding film LS equal to the constant potential V _LS .

In addition, the mutual noise of various signals for the display device can be reduced. This is explained by the following: since the LS light-shielding film has capacitive coupling with source COL lines, pixel electrodes, etc., in the case when the LS-shielding film potential is floating, the potential fluctuations of various signals for the display device affect the LS-shielding film LS ( potentials of source lines, potentials of pixel electrodes, etc.). Such potential fluctuations in the LS light shielding film further add noise to the optical sensor. In contrast, by fixing the potential of the light shielding film LS to a constant potential V _LS , fluctuations in the potential of the light shielding film LS can be eliminated, whereby the problem described above can be solved.

It should be noted that the following ratio is preferably satisfied:

V _LS ≥V _RST.H ,

where V _LS is the constant potential of the LS light-shielding film, and V _RST.H is the high-level potential of the reset signal. In addition, more preferably, the following ratio is satisfied:

V _LS ≥V _RST.H + V _{th_p} ,

where V _{th_p} is the threshold voltage of the p-channel of the diode D1. The reason for this will be described in detail below.

As shown in FIG. 6, an optical sensor according to this embodiment of the invention includes a transistor M2 in an area between source lines COLg and COLb. The diode D1 is a lateral-shaped pin diode in which the following regions are sequentially formed on a silicon film serving as a base: a p-type semiconductor region 102p, a native semiconductor region 102i, and an n-type semiconductor region 102n. The p-type semiconductor region 102p functions as the anode of the photodiode D1 and is connected to the RST line via line 108 and pins 109 and 110. The n-type semiconductor region 102n functions as the cathode of the photodiode D1 and is connected to the gate electrode 101 of the transistor M2 through the extended portion 107 silicon film, contacts 105 and 106, and line 104.

In this configuration, the RST and RWS lines are formed from the same metal as the metal of the gate electrode 101 of the transistor M2, and on the same layer in the same manner as the layer and method applied to the gate electrode 101. In addition, lines 104 and 108 are formed from the same metal as the metal of the COL line of the sources, and on the same layer in the same manner as the layer and method applied to the COL line of the sources. On the rear side of the photodiode D1, a metal film 113 is provided which functions as a light shielding film LS (see FIG. 5). As described above, the potential of the metal film 113 serving as the light shielding film is fixed to a constant potential V _LS . Therefore, the metal film 113 is connected to the line 114. The line 114 is connected to a constant voltage power supply (not shown), which is located outside the pixel region 1. It should be noted that shown in FIG. 6, a configuration in which a line 114 is provided for supplying a constant potential V _LS to a metal film 113 functioning as a light shielding film LS in parallel with a reset line RST is given as an example, but the configuration with respect to line 114 is not limited to this specific example.

In addition, as shown in FIG. 6 of FIG. 8, the capacitor C1 is formed by a wide portion 111 formed in the RWS line, an extended portion of the silicon film 107 and an insulating film (not shown) provided between the wide portion 111 and the extended portion 107. In other words, the wide portion 111 having the same potential as the potential of the RWS line, functions as the gate electrode of capacitor C1. Region 112 shown in FIG. 7 is a p + region formed by doping an n-type silicon film with a p-type impurity, for example, boron. It should be noted that when doping with a p-type impurity is performed, the wide portion 111 functions as a mask. Therefore, as shown in FIG. 8, the extended portion 107 becomes the p ⁺ region, and the silicon film portion below the wide portion 111 forms the n ^- region.

An optical sensor read operation according to this embodiment of the invention is explained hereinafter. In FIG. 9 is a signal timing chart showing a change in potential V _{INT of the} storage node from the end of the integration period to the reading period. In FIG. 9, the waveform w1, indicated by a solid line, shows the change in potential V _INT when the amount of light incident on the photodiode D1 is small. The waveform w2, indicated by the dashed line, shows the change in potential V _INT in the case when the light falls on the photodiode D1. Time t ₀ is a point in time at which the level of the read signal supplied from the RWS line starts to rise from the low level V _RWS.L. The time t ₂ is a point in time at which the level of the read signal reaches a high level V _RWS.H. The time t _S is the time at which the transistor M2 is turned on and the output of the sensor is sampled. The time t ₁ is the time at which the read signal reaches the threshold voltage V _{off of the} capacitor C1. In other words, capacitor C1 has performance characteristics that vary in accordance with the quantitative relationship between the potential that is supplied from the read signal line RWS to a wide portion 111 and the threshold voltage V _off .

In FIG. 10A and FIG. 10B is a cross-sectional diagram showing a difference in charge transfer due to the potential of the gate electrode (wide portion 111) in the capacitor C1. As shown in FIG. 9, FIG. 10A and FIG. 10B, until time t _1, capacitor C1 is always in the ON state, and after time t _1, capacitor C1 is in the OFF state. In other words, when the potential of the RWS line is equal to the threshold voltage V _off or lower, charge transfer Q _{inj occurs} under the gate electrode (wide portion 111,) as shown in FIG. 10A. However, when the potential of the RWS line exceeds the threshold voltage V _off , the charge transfer Q _inj under the gate electrode (wide portion 111) does not occur, as shown in FIG. 10B. As described above, the potential V _INT (t _S ) of the storage node at the sampling time t _S after the potential of the read signal supplied from the read signal line RWS reaches a high level V _RWS.H is expressed by formula (6) below . It should be noted that the difference ΔV _INT shown in FIG. 4 is equivalent to the difference between V _INT (t ₀ ) and V _INT (t _S ), which is equal to Q _inj / C _INT .

[Mathematical Formula 1]

(6)

(6)

Where

As shown in FIG. 9, in the optical sensor according to this embodiment, the potential difference of the storage unit, due to the difference in illumination on the light receiving surface after amplification, is greater than its potential difference at the end of the integration period. For example, the difference between the potential of the storage node after amplification during the reading period in the case of a dark state and the potential of the storage node after amplification during the reading period when light is incident at the saturation level is higher than the difference between the potential of the storage node at the end the accumulation period in the case of a dark state and the potential of the storage node at the end of the accumulation period in the case when light is incident at the saturation level. Therefore, an optical sensor having a high sensitivity and a high signal to noise ratio can be implemented.

Here, the advantages of the optical sensor according to this embodiment of the invention are explained with reference to FIG. 11 - FIG. 13. As described above, the optical sensor according to this embodiment of the invention includes a light shielding film LS (see FIG. 5) for preventing light from falling from the backlight on the surface of the photodiode D1 on the side opposite to the side of the light receiving surface, and the potential of the light shielding film is fixed equal to the constant potential V _LS . The constant potential V _LS satisfies the relation below with the high-level potential V _{RST.H of} the reset signal and the threshold voltage V _{th_p of the} p-channel of diode D1:

V _LS ≥V _RST.H + V _{th_p} .

By establishing a constant potential V _{LS of the} light shielding film LS, thus, the linearity of the photodiode D1 in the low light range can be improved. An explanation of the principles of this is given below.

In FIG. 11 is a schematic cross-sectional view showing a pin diode having a lateral structure. As shown in FIG. 11, in the case where a light-shielding film LS is provided in the vicinity of the pin diode having a lateral structure, which is the case in the optical sensor according to this embodiment, the stray capacitance created between the diode and this light-shielding film LS causes The diode functions as an element with three pins. In particular, the light-shielding film LS, the p-layer and the n-layer function respectively as a gate, anode and cathode, and it is assumed that the diode has three different modes of operation depending on the relationship between the gate potential V _LS , that is, the light-shielding film LS, the potential V _A anode and potential V _C cathode.

In FIG. 12A and FIG. 12B are graphs of the characteristic “I _d versus V _LS ”, showing differences between the three modes of operation described above. It should be noted that I _d is the photocurrent of the diode. It should be noted that the photocurrent is the current generated when light falls on the diode in accordance with the amount of incident light, and it is also called the photocurrent. In FIG. 12A is a graph showing the relationship between the potential V _{LS of the} light shielding film LS and the photocurrent I _d when the potential V _{A of the} anode is −7 V and the potential V _{C of the} cathode is 0 V. In the example shown in FIG. 12A, the behavior of the photocurrent I _d depending on the potential V _{LS of the} light-shielding film LS changes near the point V _LS = V _C + V _{th_p} as the demarcation point. Here, the operation mode in the interval V _LS ≤V _A + V _{th_p is} called "mode B", and the operation mode in the interval V _LS ≥V _A + V _{th_p is} called "mode A".

In addition, in FIG. 12B is a graph showing the relationship between the potential V _{LS of the} light shielding film LS and the photocurrent I _d in the case where the potential V _{A of the} anode is −7 V and the potential V _{C of the} cathode is −3 V. In the example shown in FIG. 12B, the behavior of the photocurrent I _d depending on the potential V _{LS of the} light-shielding film LS changes near the point V _LS = V _A + V _{th_p} as the demarcation point, as well as the behavior of the photocurrent I _d depending on the potential V _{LS of the} light-shielding film LS changes near the point V _LS = V _C + V _{th_n} as demarcation points. Here, the operation mode in the range V _LS ≤V _A + V _{th_p is} called “mode B”, the operation mode in the range V _A + V _{th_p} ≤V _LS ≤V _C + V _{th_n is} called “mode A”, and the operation mode in the range V _C + V _{th_n} ≤V _{LS is} called "mode C".

From FIG. 12A and FIG. 12B it is clear that in mode A a stably high photocurrent I _d can be obtained, and the linearity of the photocurrent with respect to illumination is excellent. Therefore, in this embodiment, the diode D1 preferably operates in mode A. In particular, in the case of V _A + V _{th_p} ≤V _LS ≤V _C + V _{th_n} (mode A), both sides of the i-layer in the diode are assumed to be on the side The p-layer and on the n-layer side are in a state in which free electrons and positive holes tend to migrate. Therefore, in mode A, the photoelectric current tends to flow unhindered through the diode, and there is a tendency for the dark current to decrease. Therefore, an excellent signal to noise ratio is obtained, and the linearity of the photocurrent with respect to illumination is improved.

On the other hand, in the case of V _LS ≤V _A + V _{th_p} (mode B), it is assumed that the boundary of the i-layer in the diode from the side of the n-layer is in a state in which free electrons and positive holes tend to migrate, whereas at the boundary of the i-layer in the diode from the side of the p-layer, the i-layer prevents the flow of electric current. In contrast, in the case of V _C + V _{th_n} ≤V _LS (mode C), it is assumed that the boundary of the i-layer in the diode on the p-layer side is in a state in which free electrons and positive holes tend to migrate, then as on its boundary from the side of the n-layer the i-layer prevents the flow of electric current. Therefore, in the cases of modes B and C, the photoelectric current cannot flow freely through the diode, and there is a tendency to increase the dark current. Therefore, an excellent signal to noise ratio cannot be obtained.

Here, the distribution of the modes A, B and C can be represented by the relation between the potential V _{A of the} anode and the potential V _{LS of the} light shielding film LS, which is shown in FIG. 13. In FIG. 13, the unshaded region is a region of mode A, the region shaded by lines from the right downward diagonal is the region of mode B, and the region shaded by lines from the left downward diagonal is the region of mode C. As described above, the region of mode A can be expressed as follows:

V _A + V _{th_p} ≤V _LS ≤V _C + V _{th_n} .

The area of mode B can be expressed as follows:

V _LS ≤V _A + V _{th_p} .

The region of mode C can be expressed as follows:

V _C + V _{th_n} ≤V _LS .

Among points T1, T2, and T3 shown in FIG. 13, T1 is a coordinate point representing V _LS and V _A at a point in time at which the level of the reset signal shown in FIG. 4, rises to a high level. Point T2 corresponds to time point t _RST shown in FIG. 4 (i.e., a point in time when the level of the reset signal is switched from a high level to a low level), and point T3 corresponds to a point in time t _RWS shown in FIG. 4 (i.e., the point in time when the level of the reset signal is switched from a low level to a high level).

Here, the triangle formed by lines extending between points T1 and T2, T2 and T3 and T3 and T1 is preferably within the region of mode A. Therefore, the following condition is preferably satisfied as a necessary condition that must be satisfied so that the value V _LS in T1 was not within the scope of mode B, but was within the scope of mode A:

V _LS ≥V _A + V _{th_p.}

It should be noted that the potential V _{A of the} anode at the beginning of the reset is equal to the high-level potential V _{RST.H of} the reset signal, and therefore, the above formula can be expressed as follows:

V _LS ≥V _RST.H + V _{th_p} .

It should be noted that the VLS value does not change during the period from T1 to T2. When the reset signal is switched to a low level at time T _RST shown in FIG. 4, the accumulation period begins (T2 in FIG. 13). Then, until the read signal level is switched to a high level at time t _RWS shown in FIG. 4 (T3 in FIG. 13), the photoelectric current corresponding to the amount of received light flows continuously, and the value of V _LS increases. After the read signal is switched to a high level at point T3, the value of V _LS returns to its original state (T1).

Since a variable capacitor is used as a capacitor C1 in this embodiment, fluctuations in the cathode potential V _C during the accumulation period are weakened compared to the case in which a conventional capacitor (which is not a variable capacitor) is used. Therefore, V _LS does not increase significantly during the accumulation period (from point T2 to point T3 in Fig. 13), which allows achieving work in the region of mode A.

In order to make the diode D1 not work in the region of mode C at the point T3, it is desirable that the gain A _{AC of the} capacitor C1 satisfy the relation represented by the following expression:

A _AC ≥VDD / (V _{th_n} -V _{th_p} ),

where VDD is the voltage of the power source of the output transistor M2. If this relation is fulfilled, then it is possible to achieve the correspondence of the range of potential variation V _{INT of the} storage node, expressed as ΔV _th = V _{th_n} ^- V _{th_p} , to the range of the output voltage from 0 V to VDD.

As described above, by setting the potential V _{LS of the} light-shielding film equal to a constant potential at which the condition V _LS ≥V _RST.H + V _{th_p} must be satisfied, it is possible to achieve the operation of the photodiode D1 in mode A from the moment the reset starts to at least , the initial stage of the accumulation period. If the diode is operating in mode B close to the start of the reset, a linearity deterioration is noticeable, especially in the low-light region, as shown in FIG. 12A and FIG. 12B. However, as explained here, due to the fact that the diode in mode A is achieved after the start of the reset, the value of the sensor output signal with a high signal-to-noise ratio and excellent linearity with changing illumination can also be obtained even during the period after the start of the reset during initial stage of the accumulation period.

Despite the fact that in the most preferred embodiment, the potential of the light-shielding film LS is set to a constant potential V _LS , which satisfies the condition V _LS ≥V _RST.H + V _{th_p} , the effect of improving the characteristics of the diode D1 can be achieved, even if the constant potential V _LS has a quantity satisfying the condition V _LS ≥V _RST.H. In addition, even if the constant potential VLS has a value that does not satisfy the condition V _LS ≥V _RST.H , the effect of improving the characteristics of the diode D1 can be achieved compared to the case when the potential of the light-shielding film LS is floating.

Since, in this embodiment, the source lines COLr, COLg, and COLb also serve as the VDD, OUT, and VSS lines, respectively, for the optical sensor described above, it is necessary to distinguish those times when the image data signals for the display device are input via the COLr lines , COLg and COLb of the sources, from the time when the output signals from the sensors are read, as shown in FIG. 14. In the example shown in FIG. 14, the sensor output is read using the horizontal blanking period after the end of the input of image data for display during the horizontal scanning period.

As shown in FIG. 1, the sensor column driver 4 includes a sensor reading circuit 41 equipped with sensors, a sensor column amplifier 42 and a sensor column scanning circuit 43. With the pixel reading circuit 41 equipped with sensors, a SOUT line is connected (see FIG. 2) for outputting the sensor output signal V _SOUT from the pixel region 1. In FIG. 1 sensor output from line SOUTj (j = 1 to N) is denoted by V _SOUTj . A sensor reading circuit 41 equipped with sensors outputs the detected peak voltage V _Sj of the sensor output signal V _SOUTj to the amplifier 42 of the sensor columns. The amplifier 42 columns of sensors includes N column amplifiers that correspond respectively to N columns of optical sensors in the region of 1 pixels. An amplifier 42 of the sensor columns amplifies the recorded peak voltage V _Sj (j = 1 to N) with an amplifier for each column, whereby it is output as V _COUT to the buffer amplifier 6. The sensor column scan circuit 43 outputs a signal CSj (j = 1 to N) selecting a column in the amplifier 42 sensor columns for sequentially connecting the column amplifiers from the amplifier 42 sensor columns to the output signal of the buffer amplifier 6.

Hereinafter, the operation of the sensor column driver 4 and the buffer amplifier 6 after reading the sensor output signal V _SOUT from the pixel region 1 with reference to FIG. 15 and FIG. 16. In FIG. 15 is a circuit diagram illustrating an internal configuration of pixel sensing circuits 41 equipped with sensors. In FIG. 16 is a signal timing chart showing the relationship between the read signal V _RWS , the output signal V _{SOUT of the} sensor and the output signal V _S from the pixel read circuit equipped with sensors. As described above, when the read signal level rises to a high level V _RWS.H , the transistor M2 becomes conductive, whereby the transistors M2 and M3 form an amplifier on the source follower. This makes it possible to store the output signal V _{SOUT of the} sensor in the capacitor C _SAM for the samples included in the pixel reading circuit 41 equipped with sensors. Therefore, as shown in FIG. 16, after the level of the read signal drops to a low level V _RWS.L , the output voltage V _S from the sensor reading circuit 41 equipped with sensors supplied to the sensor column amplifier 42 is maintained at a level equal to the maximum value of the sensor output signal V _SOUT in during a certain period (t _row ) during the selection of the corresponding row.

The following is an explanation of the operation of the sensor column amplifier 42 with reference to FIG. 17. As shown in FIG. 17, the corresponding output voltages V _Sj (j = 1 to N) of the columns are introduced from the pixel sensing circuit 41 equipped with sensors into N column amplifiers included in the amplifier 42 of the sensor columns. As shown in FIG. 17, each column amplifier is composed of transistors M6 and M7. The column selection signals C _Sj generated by the sensor column scanning circuit 43 become ON (respectively) with respect to N columns during the selection period (trow) for one row, as a result of which the transistor M6 of the corresponding one of the N column amplifiers in the 42 column amplifier is turned on sensors. Then, only the corresponding one of the output voltages V _Sj (j = 1 to N) of the columns is output through the corresponding transistor M6 as the output signal V _COUT from the amplifier 42 of the sensor columns. The buffer amplifier 6 further amplifies the V _COUT signal output from the amplifier 42 of the sensor columns and outputs it as an output signal of the V _OUT panel (optical sensor signal) to the signal processing circuit 8.

It should be noted that the sensor column scanning circuit 43 may scan the optical sensor columns one by one, as described above, but the configuration is not limited to this option. The sensor column scan circuit 43 may be configured to interlace the columns of the optical sensors. Alternatively, the sensor column scan circuit 43 may be formed as a multi-phase addressing scan circuit, such as four-phase addressing.

In the above configuration, the display device according to this embodiment of the invention receives the output signal V _{OUT of the} panel in accordance with the amount of light received by the photodiode D1 generated in each pixel in the pixel region 1. The output signal V _{OUT of the} panel is transmitted to a signal processing circuit 8, subjected thereto to analog-to-digital conversion, and stored in a storage device (not shown) as data output from the panel. This means that the same number of data sets output from the panel are accumulated in this storage device as the number of pixels (the number of optical sensors) in the region of 1 pixels. The signal processing circuit 8 performs various types of signal processing operations, for example, capturing an image and detecting the area that has been touched, using the data output from the panel that is stored in the storage device. It should be noted that in this embodiment of the invention, in the storage device of the signal processing circuit 8, the same number of data sets output from the panel are accumulated as the number of pixels (the number of optical sensors) in the region of 1 pixels, but subject to limitations, such as, for example, the capacity of the storage device, the number of data sets stored therein output from the panel is not necessarily the same as the number of pixels.

Since the wide portion 111 of the RWS line also serves as the gate electrode of the capacitor C1, the configuration according to the first embodiment of the invention has the advantage that the number of contacts (contacts 118, 119 shown in Fig. 24 with reference to the description of the third embodiment of the invention ) is smaller, whereby the size of the optical sensor circuit can be reduced in comparison with the third embodiment of the invention described below. Furthermore, in the configuration according to the first embodiment of the invention, the wide portion 111 of the RWS line is positioned so as to shield the storage node INT from the source line COL. Therefore, this configuration has the advantage of attenuating noise interference in the storage node INT from the source line COL compared to the configuration in which the source line COL is located in the layer above the storage node INT, which is, for example, in the configuration of the third embodiment inventions described below.

[Second embodiment of the invention]

The following is an explanation of a second embodiment of the present invention. Elements having the same functions as elements from the first embodiment of the invention, the explanation of which is given above, are denoted by the same reference numbers as the corresponding elements in the first embodiment of the invention, and their detailed explanations are omitted.

In FIG. 18 is an equivalent circuit diagram of an optical sensor according to this embodiment of the invention. In FIG. 19 is a signal timing chart showing a reset signal and a read signal supplied to an optical sensor according to this embodiment of the invention. In FIG. 20 is a plan view showing an exemplary planar structure of an optical sensor according to this embodiment of the invention. In FIG. 21 is an enlarged view of the region where the capacitor C1 is formed. In FIG. 22 is a schematic cross-sectional view showing a connection diagram of respective regions in an optical sensor according to this embodiment of the invention.

As shown in FIG. 18, the optical sensor according to this embodiment of the invention differs from the optical sensor of the first embodiment in that the capacitor C1 is an n-channel MOS capacitor. In addition, the diode D1 is connected in the opposite direction compared to the first embodiment of the invention. In particular, the cathode of the diode D1 is connected to the RST line, and its anode is connected to the storage node INT. Moreover, the readout transistor M2 is a p-channel TFT. In addition, as shown in FIG. 19, it is assumed that high levels and low potentials of the reset signal and the read signal are inverse compared with the first embodiment of the invention.

As shown in FIG. 20, the diode D1 is a laterally-structured pin diode in which a p-type semiconductor region 102p, an intrinsic semiconductor region 102i, and an n-type semiconductor region 102n are sequentially formed on the silicon film serving as the base, as in the first embodiment the implementation of the invention. However, the n-type semiconductor region 102n (cathode) is connected to the RST line via line 108 and contacts 109 and 110. The p-type semiconductor region 102p (anode) is connected to the gate electrode 101 of transistor M2 through an extended portion of silicon film 107, contacts 105 and 106 and line 104.

As shown in FIG. 21 and FIG. 22, the capacitor C1 is formed by a wide portion 111 formed in the RWS line, an extended portion of the silicon film 107 and an insulating film (not shown) provided between the wide portion 111 and the extended portion 107. In other words, the wide portion 111 having the same potential as the RWS line, functions as the gate electrode of capacitor C1. In this embodiment, the region 112 shown in FIG. 21 is an n + region formed by doping an n-type silicon film with an n-type impurity, such as phosphorus. When doping with an n-type impurity is performed, the wide portion 111 functions as a mask. Therefore, as shown in FIG. 22, the extended portion 107 becomes the n + region, and the silicon film portion below the wide portion 111 forms the n– region.

In the optical sensor of this embodiment of the invention having the configuration described above, the potential relationship is inverse compared with the first embodiment of the invention. Therefore, a change in the potential of the accumulation unit INT during the integration period and the reading period assumes the presence of a state obtained by reversing the state shown in FIG. 9 vertically in combination with a description of a first embodiment of the invention. Therefore, in the optical sensor of this embodiment, the potential difference of the storage unit due to the difference in illumination of the light receiving surface after amplification is also greater than this difference at the end of the integration period. For example, the difference between the potential of the storage node after amplification during the reading period in the case of a dark state and the potential of the storage node after amplification during the reading period when light falls at the saturation level is larger than the difference between the potential of the storage node at the end of the period accumulation in the case of a dark state and the potential of the storage node at the end of the accumulation period in the case when light is incident at the saturation level. As a result, an optical sensor having a high sensitivity and a high signal to noise ratio can be implemented.

In addition, through the optical sensor of this embodiment, the output of the optical sensor can also be obtained having excellent linearity when the illumination changes, as in the first embodiment of the invention, by fixing the potential of the light-shielding film LS of diode D1 equal to the constant potential V _LS and the account of establishing the value of the constant potential V _LS satisfying the following condition:

V _LS ≥V _RST.H

or preferably

V _LS ≥V _RST.H + V _{th_p} .

[Third Embodiment]

The following is an explanation of a third embodiment of the present invention. Elements having the same functions as elements from the above-described embodiments of the invention are denoted by the same reference numbers as the corresponding elements in the above-described embodiments of the invention, and detailed explanations thereof are omitted.

In FIG. 23 is an equivalent circuit diagram of an optical sensor according to this embodiment of the invention. In FIG. 24 is a plan view showing an exemplary planar structure of an optical sensor according to this embodiment of the invention. In FIG. 25, an enlarged view shows the region in which the capacitor C1 is formed. In FIG. 26 is a schematic cross-sectional view showing a connection diagram of respective regions in an optical sensor according to this embodiment of the invention.

As shown in FIG. 23, the equivalent electrical circuit of the optical sensor according to this embodiment is identical to the equivalent electrical circuit of the optical sensor of the first embodiment. However, the configuration of the capacitor 1, etc. shown in FIG. 24 - FIG. 26 is different.

As shown in FIG. 24, in the optical sensor according to this embodiment, the line from the gate electrode 101 of the transistor M2 is extended over the n-type semiconductor region 102n of the diode D1 and connected to the n-type semiconductor region 102n by the contacts 115 and 116. The line from the gate electrode 101 of the transistor M2 also extended to the upper layer of capacitor C1 and functions as gate electrode 121 of capacitor C1.

As shown in FIG. 25 and FIG. 26, a capacitor C1 is formed by a gate electrode 121, a silicon film 117 and an insulating film (not shown) between the gate electrode 121 and the silicon film 117. The gate electrode 121 has the same potential (V _INT ) as the potential of the storage unit INT. In this embodiment, the region 112 shown in FIG. 25 is an n + region formed by doping an n-type silicon film with an n-type impurity, such as phosphorus. When doping with an n-type impurity is performed, the gate electrode 121 functions as a mask. Therefore, as shown in FIG. 26, the portion of the silicon film under the gate electrode 121 forms an n-type region.

The optical sensor of this embodiment is controlled by a reset signal and a read signal, which are shown in FIG. 4 in conjunction with the description of the first embodiment of the invention, wherein the potential change of the storage unit INT during the integration period and the reading period is shown in FIG. 9 in conjunction with the description of the first embodiment of the invention. Therefore, in the optical sensor of this embodiment, the potential difference of the storage unit due to the difference in illumination of the light receiving surface after amplification is also greater than this difference at the end of the integration period. For example, the difference between the potential of the storage node after amplification during the reading period in the case of a dark state and the potential of the storage node after amplification during the reading period when light falls at the saturation level is larger than the difference between the potential of the storage node at the end of the period accumulation in the case of a dark state and the potential of the storage node at the end of the accumulation period in the case when light is incident at the saturation level. As a result, an optical sensor having a high sensitivity and a high signal to noise ratio can be implemented.

In addition, through the optical sensor of this embodiment, the output of the optical sensor can also be obtained having excellent linearity when the illumination changes, as in the first embodiment of the invention, by fixing the potential of the light-shielding film LS of diode D1 equal to the constant potential V _LS and the account of establishing the value of the constant potential V _LS satisfying the following condition:

V _LS ≥V _RST.H

or preferably

V _LS ≥V _RST.H + V _{th_p} .

[Fourth Embodiment]

The following is an explanation of a fourth embodiment of the present invention. Elements having the same functions as elements from the above-described embodiments of the invention are denoted by the same reference numbers as the corresponding elements in the above-described embodiments of the invention, and detailed explanations thereof are omitted.

In FIG. 27 is an equivalent circuit diagram of an optical sensor according to this embodiment of the invention. In FIG. 28 is a plan view showing an exemplary planar structure of an optical sensor according to this embodiment of the invention. In FIG. 29, an enlarged view shows the region where the amplification element (p-channel TFT) is formed. In FIG. 30 is a schematic cross-sectional view showing a connection diagram of respective regions in an optical sensor according to this embodiment of the invention. In FIG. 31 is an equivalent circuit diagram of a p-channel TFT optical sensor serving as an amplifying element.

In the optical sensor according to this embodiment of the invention, which is shown in FIG. 27 - FIG. 31, a p-channel TFT (transistor M4) is used as an amplifier element in place of the variable capacitor C1 used in the first to third embodiments of the invention described above. It should be noted that the control signals and the operation of the optical sensor of this embodiment, in which the transistor M4 is used as an amplifying element, are identical to the control signals and operation in the first embodiment of the invention explained above with reference to FIG. 4 - FIG. 9. Therefore, in the presence of an optical sensor according to this embodiment, the potential V _{INT of the} storage unit can also be read in the amplified state.

In addition, as shown in FIG. 28 and FIG. 29, the optical sensor according to this embodiment of the invention differs from the first embodiment of the invention in that the wide portion 111 of the RWS line is extended to such a location that it completely crosses the line 107 in the width direction. In this configuration, the optical sensor according to this embodiment has the advantage of having a shorter boundary length than the boundary length in the optical sensor according to the first embodiment.

The following is an explanation of the term “border length”. Boundary length means the length of the boundary between the amplifier element and the storage node INT. For example, in the first embodiment shown in FIG. 6 and FIG. 7, the capacitor C1 is formed by a portion where the extended portion of the silicon film 107 and the wide portion 111 of the RWS line are superposed. Therefore, in the first embodiment shown in FIG. 7, the boundary line between the amplifying element and the storage unit INT is the portion where the outer edge of the wide portion 111 of the RWS line overlaps the extended portion 107 of the silicon film, which is indicated by bold line B. In other words, in the first embodiment, the length of the boundary is the sum of the length L _CAP and 2 × W _CAP , as shown in FIG. 7. Because, as shown in FIG. 29, in the optical sensor according to this embodiment, the portion where the wide portion 111 of the RWS line overlaps the extended portion 107 of the silicon film functions as a reinforcing element, then the border length is equal to twice the width W _{TFT of} this reinforcing element (i.e. the width of the extended portion 107) .

In the first embodiment of the invention, in order to reduce the length of the boundary, it is necessary to reduce the length L _CAP , because if the capacitance of the capacitor C1 increases, then the area of the capacitor C1 stops increasing. However, in the fourth embodiment, the length of the boundary is equal to the width W _{TFT of the} extended portion 107 of the silicon film. Therefore, the length of the border can be reduced without increasing the area of placement.

The reason why a shorter border length is preferred is explained below with reference to FIG. 9 and FIG. 32. As explained in the description of the first embodiment of the invention with reference to FIG. 9, the threshold voltage V _off is a voltage of a certain level through which the level of the read signal supplied from the RWS line rises from the low level potential V _RWS.L to the high level potential V _RWS.H. Moreover, after the read signal from the RWS line reaches the threshold voltage V _off at time t ₁ , the potential V _{INT of the} storage node is preferably constant until the sampling time t _S. However, as shown in FIG. 32, during the period from time t ₁ to time t ₂ , while the level of the read signal rises, the potential V _{INT of the} storage node continuously increases due to stray capacitance between the amplifying element and the storage node. Also, during the period from the time point t ₂ , when the potential of the read signal reaches the high-level potential V _RWS.H , up to the time point t _{S, the} potential V _{INT of the} storage unit continuously increases due to the leakage current. Thus, such an increase in potential V _{INT of the} storage node after time t _{1 is} not preferable, since the effect of amplification of the potential is weakened. To attenuate the increase in potential V _INT due to stray capacitance and leakage current after time t _{1, the} length of the boundary of the amplifier element is preferably short.

Therefore, the optical sensor according to the fourth embodiment of the invention, which has a shorter boundary length of the amplifying element, is capable of attenuating the increase in potential V _INT due to stray capacitance and leakage current after time t ₁ . Thus, the optical sensor according to this embodiment is more preferable than the optical sensor according to the first embodiment.

In addition, as a modified version of the optical sensor according to the fourth embodiment, which is given as an example, a configuration can be provided in which the reinforcing element has a sufficient usable area and the length of the _TFT boundary is reduced even further by narrowing the extended portion 107 of the silicon film in width and by creating a wide portion 107a in the extended portion 107 so that the reinforcing element has a sufficient width W _CAP , as shown in FIG. 33 and FIG. 34. In this case, an equivalent circuitry of a p-channel TFT serving as an amplifier element is shown in FIG. 35. According to the configuration of this modified embodiment, given as an example, the length of the border can be reduced even more compared to the configuration shown in FIG. 27 - FIG. 31. Therefore, the increase in potential V _INT due to stray capacitance and leakage current after time t ₁ can be weakened even more. Therefore, an optical sensor having an even greater dynamic range can be implemented.

In addition, through the optical sensor of this embodiment, the output of the optical sensor can also be obtained having excellent linearity when the illumination changes, as in the first embodiment of the invention, by fixing the potential of the light-shielding film LS of diode D1 equal to the constant potential V _LS and the account of establishing the value of the constant potential V _LS satisfying the following condition:

V _LS ≥V _RST.H

or preferably

V _LS ≥V _RST.H + V _{th_p} .

[Fifth Embodiment]

The following is an explanation of a fifth embodiment of the present invention. Elements having the same functions as elements from the above-described embodiments of the invention are denoted by the same reference numbers as the corresponding elements in the above-described embodiments of the invention, and detailed explanations thereof are omitted.

In FIG. 36 is an equivalent circuit diagram of an optical sensor according to this embodiment of the invention. In FIG. 37 is a plan view illustrating an example planar structure of an optical sensor according to this embodiment of the invention. In FIG. 38, an enlarged view shows the region where the amplification element (n-channel TFT) is formed. In FIG. 39 is a schematic cross-sectional view showing a connection diagram of respective regions in an optical sensor according to this embodiment of the invention. In FIG. 40 is an equivalent circuit diagram of an n-channel TFT serving as an amplifier element.

In the optical sensor of this embodiment, an n-channel TFT (transistor M4) is used as an amplifier element instead of the n-channel MOS capacitor of the second embodiment, the explanation of which is given above. It is assumed that the high potential level and low potential level of the control signals for the optical sensor of this embodiment of the invention, in which the n-channel TFT is used as an amplifying element, are inverse to the control signals of the fourth embodiment of the invention, in which as the amplification element The element used an n-channel TFT, as described in the second embodiment with reference to FIG. 19. With these control signals in mind, the optical sensor of this embodiment of the invention is characterized in that the potential V _{INT of the} storage unit can be read in the amplified state, as explained above in the description of the first embodiment of the invention with reference to FIG. 19.

As shown in FIG. 36 and FIG. 37, in the optical sensor according to this embodiment, the diode D1 is connected in the opposite direction as compared to the fourth embodiment of the invention. In particular, the cathode of the diode D1 is connected to the RST line, and its anode is connected to the n-channel TFT. In addition, the readout transistor M2 is a p-channel TFT.

As shown in FIG. 37 and FIG. 38, the optical sensor according to this embodiment of the invention differs from the second embodiment of the invention in that the wide portion 111 of the RWS line is extended to such a location that it completely crosses the line 107 in the width direction. The optical sensor according to this embodiment has the advantage of having a shorter boundary length than the boundary length in the optical sensor according to the second embodiment, which is explained in the description of the fourth embodiment when compared with the first embodiment. In particular, as shown in FIG. 21, the boundary length of the optical sensor according to the second embodiment is L _CAP + 2 × W _CAP . On the other hand, as shown in FIG. 38, the boundary length of the optical sensor according to this embodiment is equal to the width W _{TFT of the} extended portion 107.

In the second embodiment of the invention, to reduce the length of the boundary, it is necessary to reduce the length L _CAP , while if the capacitance C1 is provided, the area of the capacitor C1 ceases to increase. However, in this embodiment, the boundary length is equal to twice the width W _{TFT of the} extended portion 107 of the silicon film. Therefore, the length of the border can be reduced without increasing the area of placement. Thus, the optical sensor according to this embodiment of the invention, characterized by a shorter length of the boundary of the amplifying element, is able to attenuate the increase in potential V _INT due to stray capacitance and leakage current after time t ₁ . Therefore, the optical sensor according to this embodiment is more preferable than the optical sensor according to the second embodiment.

In addition, as a modified embodiment of the optical sensor according to the fifth embodiment, which is given as an example, a configuration can be provided in which the amplifying element has a sufficient usable area and the length of the W _TFT boundary is reduced even more without increasing the placement area beyond by narrowing the extended portion 107 of the silicon film in width and by creating a wide portion 107a in the extended portion 107, as shown in FIG. 41 and FIG. 42. In this case, the equivalent circuitry of the n-channel TFT serving as the amplification element is that shown in FIG. 43. According to the configuration of this modified embodiment, which is given as an example, the length of the border can be reduced even more than the configuration shown in FIG. 36 - FIG. 40. Therefore, the increase in potential V _INT due to stray capacitance and leakage current after time t ₁ can be weakened even more. Therefore, an optical sensor having an even greater dynamic range can be implemented.

In addition, through the optical sensor of this embodiment, the output of the optical sensor can also be obtained having excellent linearity when the illumination changes, as in the first embodiment of the invention, by fixing the potential of the light-shielding film LS of diode D1 equal to the constant potential V _LS and the account of establishing the value of the constant potential V _LS satisfying the following condition:

V _LS ≥V _RST.H

or preferably

V _LS ≥V _RST.H + V _{th_p} .

[Sixth embodiment of the invention]

The following is an explanation of a sixth embodiment of the present invention. Elements having the same functions as elements from the above-described embodiments of the invention are denoted by the same reference numbers as the corresponding elements in the above-described embodiments of the invention, and detailed explanations thereof are omitted.

In FIG. 44 is an equivalent circuit diagram of an optical sensor according to this embodiment of the invention. In FIG. 45 is a plan view showing an exemplary planar structure of an optical sensor according to this embodiment of the invention. In FIG. 46, an enlarged view shows the region where the amplifier element (diode D2) is formed. In FIG. 47 is a schematic cross-sectional view showing a connection diagram of respective regions in an optical sensor according to this embodiment of the invention. In FIG. 48 is an equivalent circuit diagram of a diode serving as an amplifier element.

The optical sensor according to this embodiment of the invention differs from the above-described embodiments of the invention in that a diode D2 is used as an amplifying element. It should be noted that the diode D2 used here is a diode having a gate electrode in the channel. A diode D2 having a gate electrode in the channel region amplifies during the reading period using a capacitance between the gate and the diode. As shown in FIG. 44, an optical sensor according to this embodiment of the invention includes a diode D2 functioning as an amplifier element. As shown in FIG. 44 - FIG. 46, the cathode (n-type semiconductor region 107n) of the diode D2 is connected to the cathode (with the n-type semiconductor region 102n) of the diode D1, and the anode (p-type semiconductor region 107p) of the diode D2 is connected to the storage node INT.

In this configuration, the potential V _{INT of the} storage node can also be read in the amplified state, as shown in FIG. 9 in conjunction with the description of the first embodiment of the invention using the reset signal and the read signal, which are shown in FIG. 4 in conjunction with the description of the first embodiment of the invention.

In addition, the configuration according to this embodiment of the invention has two advantages described below compared to the configuration in which a p-channel TFT is used as an amplifying element, as in the fourth embodiment of the invention.

The first advantage is that the length of the border is even shorter. In particular, in the optical sensor according to this embodiment shown in FIG. 46, boundary B is present only from the region p +. Therefore, the length of the boundary is equal to the width W _{TFT of the} extended portion 107 of the silicon film. Thus, the optical sensor of this embodiment is more preferable than the optical sensor of the fourth embodiment, since the increase in potential V _INT due to stray capacitance and leakage current after time t ₁ can be weakened even more.

A second advantage is that since the cathode (n-type semiconductor region 102n) of the diode D1 is connected to the cathode (with the n-type semiconductor region 107n) of the diode D2, this connection is easier to implement compared to the fourth embodiment of the invention, in which the cathode (n-type semiconductor region 102) of the diode D1 is connected to the p-type semiconductor region.

It should be noted that the configuration shown in FIG. 49 and FIG. 50 may be taken as an exemplary modified configuration shown in FIG. 44 and FIG. 45. In FIG. 49 is an equivalent circuit diagram of an optical sensor according to a first modified embodiment of this embodiment, which is given as an example. In FIG. 50 is a plan view illustrating an exemplary planar structure of an optical sensor according to a first modified embodiment, which is given as an example. As shown in FIG. 49 and FIG. 50, the optical sensor according to the first modified embodiment of this embodiment of the invention, which is given as an example, has a configuration in which a transistor M5 for resetting is added.

The anode (p-type semiconductor region 102p) of the diode D1 is connected to the VSS line to supply a predetermined constant (DC) potential through the line 108 and the contacts 109 and 110. The gate electrode 131 of the transistor M3, intended for reset, continues from the RST line. This configuration of the first modified embodiment, which is given as an example, has the advantage of being able to more reliably reset the storage node using a reset transistor M3 that is connected to the storage node, compared with the configuration shown in FIG. 44 and FIG. 45, in which the reset is carried out through the diode D2.

In addition, as the second modified embodiment, which is given as an example, the configuration shown in FIG. 51 and FIG. 52. In FIG. 51 is an equivalent circuit diagram of an optical sensor according to a second exemplary embodiment of this embodiment of the invention. In FIG. 52 is a plan view showing an exemplary planar structure of an optical sensor according to a second modified embodiment of this embodiment, which is given as an example. The configuration shown in FIG. 51 and FIG. 52 differs from the first modified embodiment described above, which is given as an example, in that the anode (p-type semiconductor region 102p) of the diode D1 is connected to the RST line to supply a reset signal. With this configuration, there is no need to provide a separate VSS line. Therefore, this configuration has the advantage that the area of the optical sensor can be reduced in comparison with the first modified variant described above, which is given as an example.

In addition, through the optical sensor of this embodiment, the output of the optical sensor can also be obtained having excellent linearity when the illumination changes, as in the first embodiment of the invention, by fixing the potential of the light-shielding film LS of the diode D1 equal to the constant potential V _LS and setting the value of the constant potential V _LS satisfying the following condition:

V _LS ≥V _RST.H

or preferably

V _LS ≥V _RST.H + V _{th_p}

[Seventh embodiment of the invention]

The following is an explanation of a seventh embodiment of the present invention. Elements having the same functions as elements from the above-described embodiments of the invention are denoted by the same reference numbers as the corresponding elements in the above-described embodiments of the invention, and detailed explanations thereof are omitted.

In FIG. 53 is an equivalent circuit diagram of an optical sensor according to this embodiment of the invention. In FIG. 54 is a plan view showing an exemplary planar structure of an optical sensor according to this embodiment of the invention.

The optical sensor according to this embodiment of the invention has a configuration obtained by modifying the configuration of the fourth embodiment of the invention shown in FIG. 33 - FIG. 35 so that the metal film 113 serving as the light shielding film LS provided on the rear side of the diode D1 extends to a location opposite the RWS line, and through this metal film 113, the RWS line, and an insulating film (not shown) provided between by them, a capacitor C _{SER is formed} , as shown in FIG. 53 and FIG. 54. In other words, in the optical sensor according to this embodiment, the p-channel TFT (transistor M4) is used as an amplifier element, as in the fourth embodiment of the invention.

In the configuration shown in FIG. 53, the capacitor C _SER functions as a series-connected capacitor with respect to the capacitances Cc and Ca between the metal film 113 and the diode D1. Therefore, it is possible to increase only C _INT without increasing C _INT 'in the formula (6) from the first embodiment of the invention, the explanation of which is given above, and, therefore, to improve the gain effect when reading.

Since the capacitor C _{SER is} created in this way, a configuration in which a p-channel TFT is used as an amplifying element, as in this embodiment of the invention, is significantly more effective for improving the reading gain compared to a configuration in which as The amplifying element used is a capacitor of variable capacity.

In particular, in the case where the capacitor C _{SER is} combined with a configuration in which a variable capacitor C1 (the first embodiment of the invention) shown in FIG. 55A, the potential V _{INT of the} storage unit after reading is affected not only by the charges ΔQ _C from the capacitor C1, but also by the charges Q _S injected from the capacitor C _SER . Therefore, in this configuration, the capacitor C _SER stops attenuation of the reading gain.

On the other hand, as shown in FIG. 55B, in the case where the capacitor C _{SER is} combined with a configuration in which a p-channel TFT (transistor M4) is used as an amplifying element, as in this embodiment, the charges injected from the capacitor C _SER must also pass through transistor M4 when reading. Therefore, the charges (ΔQ _S ) injected from the capacitor C _SER also work to improve the gain effect along with the charges ΔQ _C.

Therefore, the optical sensor obtained by combining the C _SER capacitor with a configuration in which a p-channel TFT is used as an amplifying element, as in this embodiment of the invention, is effective for obtaining an excellent gain effect.

The above explanation relates to an example obtained by combining the capacitor C _SER with the configuration of the fourth embodiment of the invention, which is shown in FIG. 33 - FIG. 35, but the same effect can be achieved by combining the capacitor C _SER with any of the other configurations explained in the descriptions of the fourth and fifth embodiments of the invention.

[Eighth embodiment of the invention]

The following is an explanation of an eighth embodiment of the present invention. Elements having the same functions as elements from the above-described embodiments of the invention are denoted by the same reference numbers as the corresponding elements in the above-described embodiments of the invention, and detailed explanations thereof are omitted.

In FIG. 56 is an equivalent circuit diagram of an optical sensor according to this embodiment of the invention. In FIG. 57 is a plan view showing an exemplary planar structure of an optical sensor according to this embodiment of the invention. As shown in FIG. 56 and FIG. 57, in the optical sensor according to this embodiment, the diodes D1 and the capacitors C3 are ordered in parallel in a plurality of pixel regions. Capacitor C3 is a conventional capacitor (not a variable capacitor). It should be noted that the example shown in FIG. 56 and FIG. 57 has a configuration in which reading is performed from four diodes D1 by one read transistor M2, but the number of diodes D1 subjected to reading is not limited to this number.

In the example shown in FIG. 56 and FIG. 57, in the pixel region closest to the read transistor M2, a p-channel TFT (transistor M4) is formed that serves as an amplifier element, and in each of the other regions of the pixel a conventional capacitor C3 (which is not a variable capacitor) is formed.

In this configuration, in which a plurality of diodes D1 are connected in parallel, the photoelectric current can be increased. In addition, since the amplifier element is provided in the diode D1 closest to the read transistor M2 from the plurality of diodes D1, the potential of the storage node can be read in the amplified state. Thus, an optical sensor having high sensitivity can be implemented without degrading the signal-to-noise ratio. In addition, by using the p-channel TFT as an amplifier element, the boundary length can be reduced compared to the case described above in which a variable capacitor is used. This improves the amplification effect to an even greater extent.

In addition, through the optical sensor of this embodiment, the optical sensor output can also be obtained having excellent linearity when the illumination changes, as in the first embodiment of the invention, by fixing the potential of the light-shielding film LS (not shown) of the diode D1 to a constant potential V _LS and establish the value of the constant potential V _LS that satisfies the following condition:

V _LS ≥V _RST.H

or preferably

V _LS ≥V _RST.H + V _{th_p}

[Ninth embodiment of the invention]

The following is an explanation of a ninth embodiment of the present invention. Elements having the same functions as elements from the above-described embodiments of the invention are denoted by the same reference numbers as the corresponding elements in the above-described embodiments of the invention, and detailed explanations thereof are omitted.

In FIG. 58 is an equivalent circuit diagram of an optical sensor according to this embodiment of the invention. In FIG. 59 is a plan view illustrating an exemplary planar structure of an optical sensor according to this embodiment of the invention. As shown in FIG. 58 and FIG. 59, in the optical sensor according to this embodiment, the diodes D1 and the capacitors C3 are arranged in parallel in a plurality of pixel regions. Capacitor C3 is a conventional capacitor (not a variable capacitor). It should be noted that the example shown in FIG. 58 and FIG. 59 has a configuration in which reading is performed from four diodes D1 by one read transistor M2, but the number of diodes D1 subjected to reading is not limited to this number.

In the example shown in FIG. 58 and FIG. 59, a diode D2 has been created in the pixel region closest to the read transistor M2 from these four diodes D1, which serves as an amplifier element, and a conventional capacitor C3 (not a variable capacitor) is formed in each of the other regions of the pixel. In addition, in the pixel region adjacent to the read transistor M2, a reset transistor M5 is formed.

In this configuration, in which a plurality of diodes D1 are connected in parallel, the photoelectric current can be increased. In addition, since the amplifier element (diode D2) is provided in the diode D1 closest to the read transistor M2 from the plurality of diodes D1, the potential of the storage node can be read in the amplified state. Thus, an optical sensor having high sensitivity can be implemented without degrading the signal-to-noise ratio. In addition, by using the diode D2 as an amplifier element, the length of the boundary can be reduced compared with the case described above in which a capacitor of variable capacitance is used. This improves the amplification effect to an even greater extent.

In addition, through the optical sensor of this embodiment, the optical sensor output can also be obtained having excellent linearity when the illumination changes, as in the first embodiment of the invention, by fixing the potential of the light-shielding film LS (not shown) of the diode D1 to a constant potential V _LS and establish the value of the constant potential V _LS that satisfies the following condition:

V _LS ≥V _RST.H

or preferably

V _LS ≥V _RST.H + V _{th_p}

[Tenth embodiment of the invention]

The following is an explanation of a tenth embodiment of the present invention. Elements having the same functions as elements from the above-described embodiments of the invention are denoted by the same reference numbers as the corresponding elements in the above-described embodiments of the invention, and detailed explanations thereof are omitted.

In FIG. 60 is an equivalent circuit diagram of an optical sensor according to this embodiment of the invention. In FIG. 61 is a plan view illustrating an example planar structure of an optical sensor according to this embodiment of the invention. The optical sensor according to this embodiment is configured by adding a reset transistor M5 to the optical sensor according to the first embodiment, as shown in FIG. 60 and FIG. 61. The gate electrode 131 of the reset transistor M5 is a continuation of the RST line.

In this configuration, as well as in the optical sensor according to the first embodiment of the invention, the potential of the storage unit can be read in the amplified state. Thus, an optical sensor having high sensitivity can be implemented without degrading the signal-to-noise ratio.

In addition, through the optical sensor of this embodiment, the output of the optical sensor can also be obtained having excellent linearity when the illumination changes, as in the first embodiment of the invention, by fixing the potential of the light-shielding film LS of the diode D1 equal to the constant potential V _LS and setting the value of the constant potential V _LS satisfying the following condition:

V _LS ≥V _RST.H

or preferably

V _LS ≥V _RST.H + V _{th_p}

Moreover, this configuration, in which a reset transistor M5 is provided, is applicable not only to the first embodiment of the invention, but also to the second, third, fourth, fifth, seventh and eighth embodiments of the invention, and the above effect can be achieved in each of these embodiments of the invention.

The above has been an explanation of the first to tenth embodiments of the invention, but the present invention is not limited to the embodiments described above. The present invention may be modified without departing from the scope of the invention.

For example, the above description of embodiments of the invention shows a configuration in which VDD, VSS, and OUT lines are connected to the optical sensors, which also serve as source COL lines. This configuration has the advantage of a high aperture of pixels. However, since the lines for optical sensors also serve as source COL lines in this configuration, the output from the sensor circuit cannot be read during video signals to display on the screen of the display device on the source COL line. Therefore, a read signal for the output from the sensor circuit must be supplied during the flyback period, as shown in FIG. 14. Therefore, the VDD, VSS, and OUT lines for optical sensors can be created separately from the source COL lines. Although the pixel has a low aperture in this configuration, it allows excitation of the lines for optical sensors separately from the COL lines of the sources, and therefore it has the advantage that the output from the sensor circuit can be read regardless time to display the image on the screen of the display device.

INDUSTRIAL APPLICABILITY

The present invention has industrial applicability as a display device having optical sensors in the pixel region of an active matrix substrate.

Claims (17)

1. A display device comprising an optical sensor in a pixel region on an active matrix substrate, in which the optical sensor includes:
a photodetector for receiving incident light;
a reset signal line for supplying a reset signal to the optical sensor;
a read signal line for supplying a read signal to the optical sensor;
a storage unit having a potential that varies depending on the amount of light received by the photodetector during the recording period, the recording period being the period from the moment the reset signal is supplied until the read signal is supplied;
an amplifier element for enhancing the potential of the storage node in accordance with the read signal; and
a sensor switching element for sensing a potential amplified by an amplifying element and outputting this potential as an output signal of a sensor circuit to an output line,
in which the presence of a light-shielding film is provided on the side opposite to the side of the light-receiving surface relative to the photo-receiving element,
moreover, this light-shielding film is connected to a power source for supplying voltage to fix the potential of the light-shielding film to a constant potential, and the following formula is satisfied:
V _LS ≥V _RST.H ,
where V _LS is the constant potential and V _RST.H is the high-level potential of the reset signal. 2. The display device according to claim 1,
in which the photodetector is a pin diode and the following formula is satisfied:
V _LS ≥V _RST.H + V _{th_p} ,
where V _{th_p} is the threshold voltage of the p-channel pin diode. 3. The display device according to claim 1 or 2, in which the amplifying element is a capacitor of variable capacitance. 4. The display device according to claim 3, in which the variable capacitor is a MOS capacitor (a metal-oxide-semiconductor capacitor) including a read signal line, an insulating film, and a p-type semiconductor region formed in the silicon film. 5. The display device according to claim 3, in which the variable capacitor is a MOS capacitor, which includes a gate electrode of the element switching the sensor, an insulating film, and an n-type semiconductor region formed in the silicon film. 6. The display device according to claim 1 or 2, in which the amplifying element is a p-channel thin-film transistor. 7. The display device according to claim 6,
in which in the p-channel thin-film transistor, the channel region is formed in a wide area of the silicon film connecting the photodetector element and the storage node to each other, and
The gate electrode of the p-channel thin-film transistor is designed to cover this wide area. 8. The display device according to claim 1 or 2, in which the amplifying element is an n-channel thin-film transistor. 9. The display device according to claim 1 or 2, in which the amplifying element is a diode having a gate electrode in the channel. 10. The display device according to claim 1 or 2,
in which the presence of an electrode opposite the light-shielding film is provided for forming a capacitance connected in series with respect to the stray capacitance between the light-shielding film and the photodetector, and
this electrode is electrically connected to the read signal line. 11. The display device according to claim 1 or 2,
in which a plurality of photodetector elements are provided in the pixel region,
this set of photodetector elements are connected in parallel, and
an amplifying element is connected to one of the photodetector elements located at the end of the photodetector elements. 12. The display device according to claim 1 or 2,
wherein the sensor switching element is a three-pin switching element,
moreover, the gate electrode, which is one of these three conclusions, is connected to the storage node, and
one of the other two pins of these three pins is connected to the output line. 13. The display device according to claim 1 or 2,
in which a switching element is further provided for resetting the sensor switching element. 14. The display device according to claim 1 or 2,
in which the amplifier element has a threshold potential at which the state of the amplifier element switches between the on state (ON) and the off state (OFF) between the low level potential and the high level potential of the read signal. 15. The display device according to claim 1 or 2, further comprising:
the opposite substrate, which is the opposite substrate of the active matrix; and
liquid crystal located between the active matrix substrate and the opposite substrate. 16. A display device comprising an optical sensor in a pixel region on an active matrix substrate, in which the optical sensor includes:
a photodetector for receiving incident light;
a reset signal line for supplying a reset signal to the optical sensor;
a read signal line for supplying a read signal to the optical sensor;
a storage unit having a potential that varies depending on the amount of light received by the photodetector during the recording period, the recording period being the period from the moment the reset signal is supplied until the read signal is supplied;
an amplifier element for enhancing the potential of the storage node in accordance with the read signal; and
a sensor switching element for sensing a potential amplified by the amplifying element and outputting this potential as an output signal from the sensor circuit to the output line,
in which the presence of a light-shielding film is provided on the side opposite to the side of the light-receiving surface relative to the photo-receiving element, and
this light-shielding film is connected to a power source for supplying voltage to fix the potential of the light-shielding film to a constant potential. 17. The display device according to clause 16, in which the photodetector is a pin diode.

Images